A light emitting diode (LED) utilizes the principle that electrical energy is directly converted to light energy. An electric voltage is applied to both positive and negative electrode terminals of the semiconductor. When an electric current flows, electrons and holes meet and combine to release energy in the form of light. This is the light emitting principle for light emitting diodes. Depending on the different materials used in light emitting diodes, their dissimilar energy levels enable the photon energies to generate light of different wavelengths. Light emitting diodes have the advantages of compact volume, fast response rate, non-pollution and etc. These advantages allow light emitting diodes to be applied in every industrial field gradually. Also, high power light emitting diodes are progressively developed to solve the problem of insufficient brightness such that the diodes can also be applied in the field of lighting source and have a trend of substituting for conventional tungsten lamps little by little. They are the potential products for substituting conventional illumination systems in the future.
A light emitting diode is mainly comprised of a base, an LED die, an optical lens and a lens holder. The base is provided for supporting an LED die and conducting the electrodes. Structurally, the optical lens is usually fastened on the base with the lens holder, or the optical lens is bonded to the base by using an adhesive. In the structure as disclosure in US2004/0126913, the LED is assembled on a lead frame, and the optical lens is embedded in the base or on a reflector; or as disclosure in JP03-191580, the LED die and the optical lens are fastened by using the electric contacts; or as disclosure in WO2006/109113, the optical lens passes through a substrate which is fixed by way of melted plastic indexing means; or as disclosure in TW238542, a screw thread or a socket is used for fastening; or as disclosure in JP2007-080879, the optical lens is wedged on the base; other various package assemblies are as disclosure in JP2000-150968, U.S. Pat. No. 5,440,468, U.S. Pat. No. 5,068,771, US2007/002301, US2004/190304, US2007/139931, TWM313317 and the like respectively. Because an adhesive is applied between the LED die and the optical lens for fastening the optical lens and the base, the brightness is possible to be affected due to thermal aging or yellowing of the adhesive; and a lens holder applied to fasten the optical lens is a practical structure, such as described in JP60-198412. As illustrated in FIG. 1, a side view of a package structure for light emitting diode employing a lens holder is depicted. In the drawing, a package structure 1 comprises a base 10, an LED die 11, an optical lens 12 and a lens holder 13. The LED die 11 is arranged on the base 10, and the LED die is covered with the lens 12 which is located between the lens holder 13 and the base 10 and passed through an opening of the lens holder 13. The base 10 is provided with at least one through hole 101 on its surface, and the supporting stem 131 of the lens holder 13 is inserted into the through hole 101. The portion 19 of the supporting stem 131 exposed from the through hole 101 is then deformed by heat melting such that the supporting stem 131 is unable to come off the through hole, thereby achieving the purpose of fastening the optical lens 12 on the base with the lens holder 13. In addition to fasten the optical lens, such structure can be applied to suitably prevent the optical lens from separating from the base due to exceeding thermal expansion, particularly suitable for an LED with a special light pattern. The LED with a special light pattern structurally even more requires a secure joint between the optical lens and the base. However, it is difficult for such structure to accomplish the effect of positioning between the optical lens and the base. Also, the supporting stem 131 must be deformed by heat melting so it is hard to achieve the purposes of quick assembly or replacement.
With the increasingly popularization of LEDs, and application field of LEDs has become wider, a demand for the LEDs capable of generating special light patterns has arisen. The light emitting diode as shown in FIG. 2 emits a pentagonal light pattern. However, it is required for extremely exact positioning of the optical lens in the package structure for such light emitting diode capable of generating a special light pattern. Since the position of the optical lens is slightly changed or the optical lens is slightly turned, the quality of the light pattern of such LED would be affected. In the above package structure 1 of the prior art, the lens holder 13 and the optical lens 12 are fastened on the base 10 only in a manner which confines the supporting stem 131 of the lens holder 13 to the through hole 101. But after a long time of use, it is unavoidable for the package structure to be subjected to an external shake or vibration so that the portion 19 of the supporting stem exposed from the through hole cannot ever confine the supporting stem 131 to the through hole 101. This enables the lens holder 13 to be loosened and results in the movement or the rotation of the optical lens 12, which is possible to affect the light pattern of the LEDs.
Especially, if the LEDs made by using an adhesive or by the hot melt deformation of the supporting stem 131 is mounted in a light fitting or in other light emitters, its light pattern is limited to the fixation of the optical lens on the LED and unchangeable. When there is a demand for changing the light pattern, the entire LEDs must be replaced, thus causing inconvenience and an increased expense.
In order to eliminate the above-addressed problems, the inventors propose a package structure for light emitting diode based on their research for many years and plenty of practical experience, thereby accomplishing the foregoing expectations.